Selective Alkylation of Benzene with Propane over Bifunctional Pt-Heteropoly Acid Catalyst

Article abstract of DOI:10.1021/acscatal.5b01102

The alkylation of benzene with propane to yield isopropylbenzene proceeds with high selectivity over bifunctional metal-acid catalysts comprising Pt and Keggin heteropoly acid in a fixed-bed reactor at 250-350 °C and 1 bar pressure. Most efficiently the reaction occurs over Pt/H₄SiW₁₂O₄₀/SiO₂ catalyst at 300 °C, giving isopropylbenzene with 90-93% selectivity at 6-8% benzene conversion, significantly exceeding the efficiency of previously reported Pt/HZSM-5 catalyst. The alkylation proceeds through bifunctional reaction pathway including dehydrogenation of propane to propene (1) on Pt sites followed by benzene alkylation with propene (2) on acid sites. At Pt loadings above 0.5%, step 1 is at fast quasi-equilibrium and step 2 is the rate-limiting one.

Full text of DOI:10.1021/acscatal.5b01102

Subscriber access provided by Georgetown University | Lauinger and Blommer Libraries
Article
Selective alkylation of benzene with propane
over bifunctional Pt-heteropoly acid catalyst
Abdullah Alotaibi, Hossein Bayahia, Elena Kozhevnikova, and Ivan V. Kozhevnikov
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.5b01102 • Publication Date (Web): 14 Aug 2015
Downloaded from http://pubs.acs.org on August 17, 2015
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
Selective alkylation of benzene with propane over
bifunctional PtꢀHeteropoly acid catalyst
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Abdullah Alotaibi, Hossein Bayahia, Elena F. Kozhevnikova, Ivan V. Kozhevnikov*
University of Liverpool, Department of Chemistry, Liverpool L69 7ZD, UK
ABSTRACT. The alkylation of benzene with propane to yield isopropylbenzene proceeds with
high selectivity over bifunctional metalꢀacid catalysts comprising Pt and Keggin heteropoly acid
in a fixedꢀbed reactor at 250ꢀ350 oC and 1 bar pressure. Most efficiently the reaction occurs over
Pt/H4SiW12O40/SiO2 catalyst at 300 oC, giving isopropylbenzene with 90ꢀ93% selectivity at 6ꢀ8%
benzene conversion, significantly exceeding the efficiency of previously reported Pt/HZSMꢀ5
catalyst. The alkylation proceeds through bifunctional reaction pathway including
dehydrogenation of propane to propene (1) on Pt sites followed by benzene alkylation with
propene (2) on acid sites. At Pt loadings above 0.5%, step (1) is at fast quasiꢀequilibrium, and
step (2) is the rateꢀlimiting one.
KEYWORDS. Alkylation with alkanes, benzene, propane, isopropylbenzene, Ptꢀheteropoly acid
catalysts.
ACS Paragon Plus Environment
1

ACS Catalysis
Page 2 of 24
1
2
3
4
1. Introduction
5
6
7
8
9
Effective functionalization of light alkanes constituting natural gas, such as methane, ethane and
propane, has long been and still remains one of the greatest challenges for catalysis science.1,2
Involving alkanes in reactions with other organic molecules, e.g., aromatic hydrocarbons, is
important direction of light alkane utilization. The alkylation of benzene with ethane and propane
to produce ethylbenzene (EtPh) and isopropylbenzene (iPrPh)) has attracted particular interest.3
EtPh and iPrPh are the key intermediates in manufacturing styrene and phenol and produced
commercially on a very large scale by the wellꢀestablished acidꢀcatalyzed alkylation of benzene
by alkenes, viz. ethene and propene.4 The replacement of ethene and propene by abundant and
inexpensive alkanes would lead to more cost effective and environmentally benign production of
these commodity chemicals.4
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Olah et al.5 pioneered the alkylation of benzene with light alkanes in liquid superacid media to
obtain EtPh and iPrPh in low yields (1.0 and 1.4%) at 25 oC in 24 h reaction time. Later more
efficient and environmentꢀfriendly solid catalysts had been discovered for the alkylation of
benzene with ethane6ꢀ14 and propane15ꢀ20 in the gas phase. These catalysts comprise zeolites
modified with metals such as Pt, Pd, Re, Ga or Zn and operate via bifunctional pathway, which
includes alkane dehydrogenation on metal sites to form alkene and H2 followed by benzene
alkylation with the alkene on acid sites (Scheme 1). Best results have been achieved using Ptꢀ
modified HZSMꢀ5 zeolites (MFI structure). Lukyanov et al.9 have reported >90% EtPh
selectivity at a close to equilibrium benzene conversion of 11.6% in the alkylation of benzene
with ethane over 1%Pt/HZSMꢀ5 (Si/Al = 36) at 370 oC, [C6H6]/[C2H6] = 1:9 mol/mol and 1 bar
pressure. The yield can be further increased by adding a hydrogen acceptor to shift equilibrium
ACS Paragon Plus Environment
2

Page 3 of 24
ACS Catalysis
1
2
3
4
5
6
in step (1), however this effect decreases with time on stream due to saturation of acceptor
capacity.12
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 1. Alkylation of benzene by propane via bifunctional catalyzed pathway.
The alkylation of benzene with propane, in contrast to the reaction with ethane, has proved to be
more difficult to achieve high selectivity. Smirnov et al.16 have studied this reaction with a range
of Pt/HZSMꢀ5 catalysts (Si/Al = 25ꢀ160) with and without addition of Zr2Fe as a hydrogen
acceptor to shift propane dehydrogenation equilibrium. In the presence of Zr2Fe, iPrPh has been
obtained with 32% selectivity at 14.4% conversion (4.6% yield) using 0.22%Pt/HZSMꢀ5 (Si/Al
= 160) as the catalyst at 350 oC, 1 bar pressure and [C6H6]/[C3H8] = 1:1. In the absence of Zr2Fe,
the conversion dropped to 6.6%, with the selectivity unchanged (2.1% iPrPh yield). It should be
noted that the main product was nPrPh (50% selectivity) rather than the favourable from the
carbenium ion mechanism iPrPh. This points to the product shape selectivity control imposed by
HZSMꢀ5, i.e., iPrPh formed initially possibly isomerized on HZSMꢀ5 proton sites to nPrPh
possessing higher diffusion mobility within zeolite micropores. Other alkylation products such as
MePh, EtPh and unidentified C9ꢀC11 alkylarenes were also formed. MePh and EtPh are
thermodynamically more favourable than iPrPh and probably arise from cracking reactions on
zeolite acid sites.16 It is likely, therefore, that the poor selectivity of benzene alkylation with
propane on Pt/HZSMꢀ5 is the result of the confinement of product molecules within zeolite
micropores causing their isomerization and cracking to form primarily nPrPh together with the
ACS Paragon Plus Environment
3

ACS Catalysis
Page 4 of 24
1
2
3
4
5
6
range of byꢀproducts observed. In this regard, it is conceivable that bifunctional catalysts based
on strong solid acids possessing larger pores could improve reaction selectivity.
7
8
9
In the last decade, we have investigated bifunctional heterogeneous catalysis by Keggin
heteropoly acids (HPAs) modified with platinum group metals in a wide range of gasꢀ and
liquidꢀphase reactions.21ꢀ24 HPAs are commercially available solid materials possessing very
strong Brønsted acidity, stronger than zeolites and common mineral acids.25,26 These have found
many applications in catalysis, including several industrial processes.26 Supporting HPA on
oxide supports provides solid acid catalysts with wide range of pore geometries, e.g., SiO2ꢀ
supported HPAs possess both strong acidity and mesoporous structure.26 Here we demonstrate
highly efficient bifunctional catalysis by Ptꢀmodified Keggin HPA H4SiW12O40 for the alkylation
of benzene with propane to give iPrPh with >90% selectivity.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2. Experimental
2.1. Chemicals and catalysts. Heteropoly acid hydrates H3PW12O40 (HPW, 99%) and
H4SiW12O40 (HSiW, 99.9%) containing 20ꢀ28 H2O molecules per Keggin unit were purchased
from SigmaꢀAldrich. The amount of crystallization water in heteropoly acids was determined by
+
TGA. Zeolite NH4 ꢀZSMꢀ5 (Si/Al = 18, specific surface area SBET = 400 m2gꢀ1) was from
o
Zeolyst International. It was converted into the H+ form by air calcination at 500 C for 6 h.
Carbonꢀsupported platinum 10%Pt/C was from Johnson Matthey (7.0% Pt content in dried
catalyst from ICPꢀAES analysis). Pt(acac)2 and Pt(NH3)4(NO3)2 were purchased from Sigmaꢀ
Aldrich. Propane, N2 and H2 gases (all >99% purity) were supplied by the British Oxygen
ACS Paragon Plus Environment
4

Page 5 of 24
ACS Catalysis
1
2
3
4
5
6
Company. From GC analysis, the propane contained C3H8 (99.20%), C2H6 (0.76%), C3H6
(0.01%), C4H10 (0.03%) and methane (0.004%).
7
8
9
Supported HPA catalysts were prepared by wet impregnation of oxide supports with an aqueous
HPA solution and dried at 150°C/10ꢀ3 kPa for 1.5 h.27,28 The oxide supports P25 titania
(anatase/rutile = 3:1) and Aerosil 300 silica (SBET = 300 m2gꢀ1) were from Degussa. ZrO2 and
Nb2O5 oxides were prepared inꢀhouse27,28 and calcined at 400 oC in air for 5 h.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
PtꢀHPA bifunctional catalysts were prepared by wet impregnation of acidic component, e.g.,
25%HPA/SiO2, with 0.02 M Pt(acac)2 solution in benzene at room temperature for 1 h, followed
by slow evaporation of benzene in a rotary evaporator at room temperature.24 The catalyst was
dried under vacuum at 150 oC/10ꢀ3 kPa and then reduced in oven by hydrogen flow at 250 oC for
2 h. 0.31%Pt/HZSMꢀ5 was prepared by the literature procedure22 involving adsorption of Pt(II)
on to zeolite from 0.01 M aqueous solution of Pt(NH3)4(NO3)2 followed by washing with
distilled water, air calcination at 450 oC for 2 h and reduction by H2 at 400 oC for 2 h. The Pt
loading quoted was determined by the ICPꢀAES analysis. Physical mixtures of 7%Pt/C with
25%HPA/SiO2 or HZSMꢀ5 containing 0.7% of Pt were prepared by grinding a 1:9 w/w mixture
of these compounds.
2.2. Techniques. BET surface area and porosity of catalysts were determined from nitrogen
physisorption measured on a Micromeritics ASAP 2010 instrument at −196 oC. Before
measurement, the samples were evacuated at 250 oC for 2 h. Thermogravimetric analyses were
carried out using a Setaram TGꢀDSC 111 differential scanning calorimeter. DRIFT (diffuse
reflectance infrared Fourier transform) spectra of catalysts were recorded on a Nicolet Nexus
ACS Paragon Plus Environment
5

ACS Catalysis
Page 6 of 24
1
2
3
4
5
6
7
8
9
FTIR spectrometer using powdered catalyst mixtures with KBr. Temperature programmed
reduction (H2ꢀTPR) of catalysts was carried out on a Micromeritics TPD/TPR 2900 apparatus
equipped with a thermal conductivity detector. Catalyst samples (20ꢀ30 mg) were heated up to
800 oC at a rate of 10 oC minꢀ1 in a H2ꢀN2 (5:95) gas flow (60 mL minꢀ1). ICPꢀAES elemental
analysis was carried out on a Spectro Ciros emission spectrometer. The amount of carbon
deposited on postꢀreactor catalysts was measured by combustion elemental analysis.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 1. Catalyst characterization
a
Catalyst
SBET
Pore
Pore sizec Dd
de
∆Hf
volumeb
m2gꢀ1
Å
%
nm
kJ molꢀ1
cm3gꢀ1
7%Pt/C
ꢀ
ꢀ
ꢀ
39
ꢀ
2.3
ꢀ
25%HPW/SiO2
25%HSiW/SiO2
198
191
1.00
0.84
0.92
0.88
0.21
1.02
1.00
0.20
0.11
0.09
203
177
195
194
24
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1%Pt/25%HPW/SiO2 189
1%Pt/25%HSiW/SiO2 181
27
24
3.3
ꢀ
3.8
ꢀ
0.31%Pt/HZSMꢀ5
15%HSiW/SiO2
15%HPW/SiO2
15%HPW/TiO2
15%HPW/Nb2O5
15%HPW/ZrO2
369
221
202
45
60
1.5
ꢀ
ꢀ
185
169
174
34
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ154
ꢀ154
ꢀ143
ꢀ132
ꢀ121
ꢀ
ꢀ
ꢀ
ꢀ
126
109
36
aBET surface area. bSingle point total pore volume. cAverage BET pore diameter. dPt dispersion
in catalysts determined from CO chemisorption. ePt particle size calculated from equation d (nm)
= 0.9/D. fInitial enthalpy of ammonia adsorption at 150 oC (±3 kJ molꢀ1).27,28
ACS Paragon Plus Environment
6

Page 7 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
Pt dispersion, D, defined as the fraction of metal at the surface, D = Pts/Pttotal, was determined by
pulse chemisorption of CO in He flow at 50 oC using Micromeritics TPD/TPR 2900 instrument
(20 mg catalyst sample, 50 ꢁL pulses of pure CO, adsorption stoichiometry Pts:CO = 1). The
average diameter of metal particles, d, was calculated from the empirical equation d (nm) =
0.9/D.29 Table 1 shows the texture and Pt dispersion of the catalysts studied.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.3. Catalyst testing. The alkylation of benzene with propane was carried out in the gas phase at
250ꢀ350 oC and an inlet C6H6/C3H8 molar ratio of 1:9 under atmospheric pressure in a quartz
fixedꢀbed downꢀflow reactor (9.0 mm internal diameter) with online GC analysis (Varian 3800
instrument with a 30 m x 0.32 mm x 0.5 ꢁm Zebron ZBꢀWAX capillary column and a flame
ionisation detector) (Figure S1, Supporting Information). For more accurate analysis of C1ꢀC3
hydrocarbon products, a 60 m x 0.32 mm GSꢀGasPro capillary column was used, which allowed
for complete separation of these hydrocarbons. The temperature in the reactor was controlled by
a Eurotherm controller using a thermocouple placed at the top of the catalyst bed. Benzene was
fed into the gas flow by passing propane flow controlled by a Brooks mass flow controller
through a stainless steel saturator, which held liquid benzene at 20 oC to maintain the chosen
reactant partial pressure of 10 kPa.30 The downstream gas lines and valves were heated to 150 oC
to prevent substrate and product condensation. The reactor was packed with 0.20 g catalyst
powder of 45ꢀ180 ꢁm particle size. The gas feed entered the reactor at the top at a flow rate of 10
mL minꢀ1 (space time W/F = 80 g h molꢀ1, where W (g) is the catalyst weight and F (mol hꢀ1) is
the molar flow rate of benzene). Prior to reaction, the catalyst was preꢀtreated in H2 for 1 h at the
reaction temperature. The downstream gas flow was analysed by the onꢀline GC to obtain
benzene conversion and product selectivity. The selectivity to alkylbenzenes was defined as
ACS Paragon Plus Environment
7

ACS Catalysis
Page 8 of 24
1
2
3
4
5
6
7
8
9
moles of product formed per one mole of benzene converted and quoted in mole per cent. The
mean absolute percentage error in conversion and selectivity was ≤ 10% and the carbon balance
was maintained within 95%.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3. Results and discussion
3.1. Thermodynamic analysis. The alkylation of benzene with propane via bifunctional
pathway combines propaneꢀtoꢀpropene dehydrogenation (1) and benzene alkylation with propene
thus formed (2) (Scheme 1). Step (1) is thermodynamically unfavourable, whereas step (2) is
favourable one. Tungsten HPAs are active catalysts for the alkylation of benzene with propene
(step (2))31 as well as for the reverse reaction of iPrPh cracking.32 Figure 1 shows the Gibbs free
energy (ꢂG) for these steps calculated from thermodynamic data33ꢀ36 (see SI for details). At 300
oC and 1 bar pressure, equilibrium conversion of propane in step (1) is only 0.55%. For benzene
alkylation with propane, ꢂG is positive at 30ꢀ35 kJ molꢀ1 in the temperature range of 25ꢀ800 oC.
Equilibrium conversion of benzene at 300 oC and [C6H6]/[C3H8] molar ratio of 1:1 is 2.8%. At
the ratio [C6H6]/[C3H8] = 1:9 applied in this work, it increases to 8.2% (Figure 1).
Table 2 shows the experimental conversion values for propane dehydrogenation (1) over
bifunctional catalyst 1%Pt/25%HSiW/SiO2 at 300ꢀ400 oC under typical reaction conditions
applied for benzene alkylation in this work. It is evident that the experimental values of propane
conversion are practically equal, within the accuracy of measurement, to the calculated
equilibrium values, which indicates that the dehydrogenation reaction is fast in this system. On
top of that, the amount of methane and ethane present in propane flow did not change hence
propane cracking did not occur in this temperature range. Propane aromatization did not occur
either, as no aromatic compounds were found amongst the products.
ACS Paragon Plus Environment
8

Page 9 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
100
80
1.0
0.8
0.6
0.4
0.2
0.0
2
60
6
3
40
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
20
0
4
1
-20
-40
-60
-80
5
0
100
200
300
400
500
600
700
800
900
Temperature (oC)
Figure 1. Gibbs free energy (ꢂG) and equilibrium conversion (X) for dehydrogenation of
propane (undiluted C3H8) and alkylation of benzene with propane as a function of temperature at
1 bar pressure: (1) ꢂG and (2) X for C3H8 = C3H6 + H2; (3) ꢂG and (4) X at [C6H6]/[C3H8] = 1:9
and (5) X at [C6H6]/[C3H8] = 1:1 for C6H6 + C3H8 = iPrPh + H2; (6) ꢂG for C6H6 + C3H6 = iPrPh.
a
Table 2. Propane dehydrogenation over 1%Pt/25%HSiW/SiO2
Temperature (oC)
300
350
400
Experimental propane conversion (%)b
Calculated equilibrium conversion (%)
0.48
0.55
1.93
1.68
4.56
4.25
aCatalyst (0.20 g) preꢀtreated in situ at 300 oC/1 h in H2 flow, 10 mL minꢀ1 propane flow rate,
W/F = 80 g h molꢀ1, 1 bar pressure, 1 h time on stream. bInlet gas contained propane (99.20%),
propene (0.01%), ethane (0.76%), butane (0.03%) and methane (0.004%); methane and ethane
content did not change in the downstream flow.
ACS Paragon Plus Environment
9

ACS Catalysis
Page 10 of 24
1
2
3
4
5
6
7
8
9
3.2. Alkylation of benzene over Pt/HZSM-5. It is essential to compare new Pt/HPA and
previously reported Pt/HZSMꢀ5 catalysts at the same reaction conditions. Therefore, first we
tested Pt/HZSMꢀ5 for benzene alkylation with propane in our system at 300 oC, contact time W/F
= 80 g h molꢀ1 and [C6H6]/[C3H8] = 1:9. Representative results are given in Table 3. Supported
bifunctional catalyst 0.31%Pt/HZSMꢀ5 gave 16.4% iPrPh selectivity at 19.9% conversion (3.3%
benzeneꢀbased yield), with nPrPh (33.8%) and MePh (21.5%) formed as the main products. It
should be noted that this catalyst showed stable performance for over 8 h on stream (Figure 2). In
the absence of Pt, HZSMꢀ5 gave only 1.1% benzene conversion with a similar iPrPh selectivity
of 14.2%, which is in agreement with the previous report.16 The reaction with Ptꢀfree catalyst
probably occurs through carbonium ion intermediate or transition state formed by propane
protonation with the zeolite.16 Uniform physical mixture 7%Pt/C + HZSMꢀ5 (1:9 w/w) with
0.7% Pt content showed practically the same activity as the 0.31%Pt/HZSMꢀ5 catalyst at 19.0%
conversion and 12.8% iPrPh selectivity (Figure S2), with MePh (30.8%), nPrPh (24.3%) and
EtPh (16.5%) formed as the main products (Table 3). This disagrees with Smirnov et al.16 who
found a 4ꢀfold decrease in catalyst activity when using a 1:1 w/w physical mixture of
0.3%Pt/CeO2 and HZSMꢀ5 (Si/Al = 25ꢀ160) instead of 0.22ꢀ0.29%Pt/HZSMꢀ5 at 350 oC and
[C6H6]/[C3H8] = 1:1. At least partly, this may be explained by the decrease in Pt loading in the
Pt/CeO2 + HZSMꢀ5 physical mixture in comparison with the supported Pt/HZSMꢀ5 catalyst.
Only when we used two catalyst beds, 7%Pt/C (top) and HZSMꢀ5 (bottom) (1:9 w/w) separated
by ~1 mm layer of silica, a 4ꢀfold drop in benzene conversion was predictably observed,
although the selectivity pattern did not change (Table 3, Figure S3). This supports the view that
the selectivity of benzene alkylation with propane over Pt/HZSMꢀ5 catalyst is controlled by acidꢀ
catalyzed transformations within zeolite microporous structure.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
10

Page 11 of 24
ACS Catalysis
1
2
Table 3. Alkylation of benzene with propane via bifunctional catalyzed pathwaya
3
4
5
6
7
8
9
Catalyst
Conversionb
(%)
Aromatic selectivity (%)c
MePh EtPh iPrPh nPrPh C9+
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
HZSMꢀ5
1.1 (2)
0.2 (2)
0.1 (2)
19.9 (8)
19.0 (6)
5.1 (7)
3.1 (3)
4.0 (3)
2.0 (3)
3.8 (4)
25.5
22.8 14.2
1.5 81.0
24.6
3.1
12.9
14.4
8.2
25%HSiW/SiO2
0
0
d
7%Pt/C+SiO2
0
37.2
54.6
33.8
24.3
22.6
2.1
0.31%Pt/HZSMꢀ5
21.5
30.8
26.5
0
6.0 16.4
16.5 12.8
31.2 12.8
0.8 75.7
0.8 81.6
3.0 81.9
1.6 85.7
0.5 89.2
0.5 90.4
0.7 92.6
22.4
15.7
6.9
7%Pt/C+HZSMꢀ5 (0.7%Pt)d
7%Pt/C+HZSMꢀ5 (0.7%Pt)e
1%Pt/25%HPW/SiO2
21.4
14.7
12.9
10.2
7.8
f
1%Pt/25%HSiW/SiO2
0
2.9
g
1%Pt/25%HSiW/SiO2
0
2.2
7%Pt/C+25%HPW/SiO2 (0.7%Pt)d
0
2.6
7%Pt/C+25%HSiW/SiO2 (0.7%Pt)d 5.5 (6)
7%Pt/C+25%HSiW/SiO2 (0.7%Pt)e 7.6 (9)
7%Pt/C+25%HSiW/SiO2 (0.7%Pt)h 6.2 (15)
0
2.4
0
3.0
6.0
0
2.7
4.2
aReaction conditions: 300 oC, 1 bar pressure, 0.20 g catalyst, inlet molar ratio C6H6/C3H8 = 1:9,
10 mL minꢀ1 flow rate, W/F = 80 g h molꢀ1; in situ catalyst preꢀtreatment at 300 oC/1 h in H2
flow, 10 mL minꢀ1). bAverage conversion of benzene since steady state reached during time on
stream (h) given in round brackets. cSelectivity to aromatic products including unidentified C9+
alkylbenzenes. dUniform physical mixture 7%Pt/C (0.02 g) + HZSMꢀ5, 25%HSiW/SiO2 or SiO2
(0.18 g). eTwo catalyst beds: 7%Pt/C (0.02 g, top bed) and 25%HSiW/SiO2 or HZSMꢀ5 (0.18 g,
bottom bed). 1.2% coke content in the catalyst after reaction. gAt 250 oC. hTwo catalyst beds:
f
ACS Paragon Plus Environment
11

ACS Catalysis
Page 12 of 24
1
2
3
4
5
6
7%Pt/C (0.02 g, top bed) and 0.18 g 25%HSiW/SiO2 (0.18 g, bottom bed) separated with ca. 1
mm SiO2 layer.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
100
80
60
40
20
0
40
30
20
10
0
MePh
EtPh
iPrPh
nPrPh
Conversion
0
100
200
300
400
500
600
Time (min)
Figure 2. Time course for alkylation of benzene with propane over 0.31%Pt/HZSMꢀ5 (Si/Al =
18) (0.20 g catalyst, 300 oC, 1 bar pressure, inlet molar ratio C6H6/C3H8 = 1:9, 10 mL minꢀ1 flow
rate, W/F = 80 g h molꢀ1; inꢀsitu catalyst preꢀtreatment at 300 oC/1 h in H2 flow, 10 mL minꢀ1).
3.3. Alkylation of benzene over Pt/HPA catalysts. Bulk tungsten HPAs possess very strong
proton sites.25,26 The initial enthalpy of ammonia adsorption (∆H) for bulk HPW and HSiW have
been reported to be ꢀ19727,28 and ≤ ꢀ16037 kJ molꢀ1, respectively. The acid sites of MFI zeolites
are weaker, ∆H = 131ꢀ150 kJ molꢀ1 (Si/Al = 20ꢀ70), from ammonia adsorption microcalorimetry
and TPD.38 However, supporting HPA reduces the acid strength because of HPAꢀsupport
interaction27,28 (Table 1).
ACS Paragon Plus Environment
12

Page 13 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
Initial testing of supported HPA catalysts modified with platinum group metals showed that Pt
catalysts were more active than Pd ones in the alkylation of benzene with propane, in agreement
with previous studies.3 Amongst Keggin HPAs tested, H4SiW12O40 (HSiW) gave the best
performance, followed by H3PW12O40 (HPW). Bulk Cs salt C2.5H0.5PW12O40, which is widely
used as a strong solid acid catalyst25,26 showed very low activity. Predictably, the best catalyst
support was found to be SiO2; other oxide supports such as TiO2, Nb2O5 and ZrO2 gave lower
benzene conversions (see below) probably due to decreasing the acid strength of HPA.27 Best
performance in benzene alkylation with propane gave the catalysts comprising 0.5ꢀ1% Pt metal
and 25%HSiW/SiO2. These were mesoporous materials with SBET = 181ꢀ191 m2gꢀ1 and pore
diameters of 177ꢀ194 Å (Table 1). For 1%Pt/25%HSiW/SiO2, the N2 adsorption isotherm and
pore size distribution are shown in Figures S4 and S5. Benzene conversion increased with
temperature from 250 to 300 oC. Further temperature increase to 350 oC did not produce any
increase in conversion probably due to catalyst deactivation by coking. Therefore, further
catalyst testing was carried out at 300 oC. Representative results are shown in Table 3.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The reaction with either Pt or HSiW as monofunctional catalysts gave a very low benzene
conversion of 0.1ꢀ0.2% (Table 3). This clearly demonstrates that the alkylation of benzene with
propane occurs through bifunctional metalꢀacid catalysis (Scheme 1).
The most striking feature of the alkylation over Pt/HPA catalysts is its high selectivity to iPrPh,
which is the preferred alkylation product from the classical carbenium ion mechanism. For the
Pt/HSiW/SiO2 catalysts, the iPrPh selectivity was in the range of 83ꢀ93% (cf. 13ꢀ16% with
Pt/HZSMꢀ5, Table 3). The main byꢀproducts were unidentified C9+ alkylarenes, with only small
amounts of EtPh (0.5ꢀ1.6%) and nPrPh (2.1ꢀ3.0%) formed. MePh was not observed at all
amongst the products. This is in agreement with the results on the alkylation of benzene by
ACS Paragon Plus Environment
13

ACS Catalysis
Page 14 of 24
1
2
3
4
5
6
7
8
9
propene over supported HPA, which gives high selectivity to iPrPh with only negligible amount
of nPrPh formed.31 The difference in reaction selectivity between Pt/HPA/SiO2 and Pt/HZSMꢀ5
catalysts indicates that with Pt/HZSMꢀ5 the alkylation is controlled by zeolite shape selectivity,
whereas with Pt/HPA/SiO2 the reaction is likely to occur under kinetic control. It is worth noting
that Ptꢀfree monofunctional acid catalysts HSiW/SiO2 and HZSMꢀ5 exhibited the same
selectivity pattern (Table 3), which further strengthens this point.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1%Pt/25%HSiW/SiO2 catalyst gave 81.6% iPrPh selectivity, with benzene conversion gradually
decreasing from 7.5% to less than 4% over 3 h on stream. This can be explained by catalyst
coking; 1.2% of coke was found in the spent catalyst, which could block Pt and/or HPA proton
sites in the catalyst. The loss of acidity due to HPA reduction can be ruled out as the cause of
catalyst deactivation since the HPA reduced only above 500 oC (see the H2ꢀTPR in Figure S6 and
S7). The structural integrity of the HPA was also maintained during reaction as evidenced by the
DRIFT spectra of fresh and spent catalysts, showing that the Keggin structure remained intact
(Figure S8). The fact that HPW despite its superior acid strength was a less efficient partner in
the Pt/HPA catalyst than HSiW may be the result of relatively more intense coking of HPW.
Physical mixture of 7%Pt/C + 25%HSiW/SiO2 (1:9 w/w) with 0.7% Pt content exhibited more
stable performance with a higher average conversion of 5.5% over 6 h on stream and 85.7%
iPrPh selectivity. Figure 3 shows the time course for this reaction, which is typical of Pt/HSiW
bifunctional catalysts. It is seen that iPrPh selectivity increases during first 2 h on stream to reach
steadyꢀstate value at about 90%. At the same time, benzene conversion gradually decreases to
level off at about 5%. This behaviour may be explained by catalyst coking.
ACS Paragon Plus Environment
14

Page 15 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
100
80
60
40
20
0
40
30
20
10
0
MePh
EtPh
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
iPrPh
nPrPh
Conversion
0
50
100
150
200
250
300
350
Time (min)
Figure 3. Time course for alkylation of benzene with propane over 7%Pt/C (0.02 g) + 25%
HSiW/SiO2 (0.18 g) physical mixture (0.20 g total catalyst weight, 0.7% Pt; 300 oC, 1 bar
pressure, inlet molar ratio C6H6/C3H8 = 1:9, 10 mL minꢀ1 flow rate, W/F = 80 g h molꢀ1; inꢀsitu
catalyst preꢀtreatment at 300 oC/1 h in H2 flow, 10 mL minꢀ1).
Even better conversion stability and higher iPrPh yield gave twoꢀbed catalysts comprising
7%Pt/C and 25%HSiW/SiO2 beds either unseparated or separated with ~1 mm layer of SiO2
(Table 3). The unseparated twoꢀbed catalyst gave 7.6% conversion over 9 h on stream (Figure 4)
with 90.4% iPrPh selectivity (6.9% yield). This yield is quite close to the equilibrium value
(8.2%) and significantly higher than that reported so far (cf. 4.6% yield with hydrogen acceptor
and 2.1% without it16). The catalyst with silicaꢀseparated beds exhibited stable 6.2% benzene
conversion for 13 h on stream with iPrPh selectivity of 92.6%, the highest achieved in this work
(Figure S9). The high activity of mixed and twoꢀbed catalysts indicates that the reaction is not
limited by migration of intermediates between metal and acid sites. The better performance
stability of these catalysts in comparison to the supported 1%Pt/25%HSiW/SiO2 catalyst may be
explained by their better resistance to coking.
ACS Paragon Plus Environment
15

ACS Catalysis
Page 16 of 24
1
2
3
4
5
6
7
8
100
80
60
40
20
0
40
30
20
10
0
9
MePh
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
EtPh
iPrPh
nPrPh
Conversion
0
100
200
300
400
500
Time (min)
Figure 4. Time course for alkylation of benzene with propane over twoꢀbed catalyst 7%Pt/C
(0.02 g, top bed) + 25% HSiW/SiO2 (0.18 g, bottom bed) (0.20 g total catalyst weight, 0.7% Pt;
300 oC, 1 bar pressure, inlet molar ratio C6H6/C3H8 = 1:9, 10 mL minꢀ1 flow rate, W/F = 80 g h
molꢀ1; inꢀsitu catalyst preꢀtreatment at 300 oC/1 h in H2 flow, 10 mL minꢀ1).
The apparent activation energy for benzene alkylation with 1%Pt/25%HSiW/SiO2 was roughly
estimated to be 50 kJ molꢀ1 (from the results at 250 and 300 oC, Table 3). This value indicates
that the reaction was not affected by mass transport limitations, thus supporting the view that the
reaction selectivity was not controlled by pore diffusion.
ACS Paragon Plus Environment
16

Page 17 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
100
80
60
40
20
0
10
8
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
6
4
iPrPh selectivity
Conversion
2
0
0
0.2
0.4
Pt loading (%)
0.6
0.8
Figure 5. Effect of Pt loading on conversion and iPrPh selectivity of benzene alkylation over
7%Pt/C+25%HSiW/SiO2 catalyst at 300 oC.
Further mechanistic evidence was obtained from examination of effects of Pt loading and HPA
acid strength on the rate of benzene alkylation. Figure 5 shows the effect of Pt loading on
benzene conversion and iPrPh selectivity for the reaction over mixed catalyst 7%Pt/C +
25%HSiW/SiO2. Both parameters increase with Pt loading and reach a plateau at a Pt loading of
0.5%. This indicates that at Pt loading above 0.5% propane dehydrogenation step (1) is at fast
quasiꢀequilibrium. It should be noted that Pt dispersion was not varied here since the same
7%Pt/C catalyst was used in these experiments.
The catalytic activity of HPA in the conventional alkylation of benzene by propene has been
found to increase with HPA acid strength.31 Here the effect of HPA acid strength on catalyst
activity in benzene alkylation by propane was assessed using mixed catalysts 7%Pt/C +
15%HPA/Support (1:9 w/w) at 0.7% Pt and 15% HPA loading and SiO2, TiO2, Nb2O5 and ZrO2
as the HPA supports (Table 4). We used the mixed rather than twoꢀbed catalysts because the
ACS Paragon Plus Environment
17

ACS Catalysis
Page 18 of 24
1
2
3
4
5
6
7
8
9
former allowed better reproducible conversions to be obtained. The acid strength of the
15%HPA/Support catalysts has been determined previously by microcalorimetry of ammonia
adsorption;27,28 it decreases in the order of supports SiO2 > TiO2 > Nb2O5 > ZrO2 (Table 1)
owing to increasing interaction between HPA and support in this series.27 As seen from Table 4,
the conversion of benzene also decreases in this order, although reaction selectivity remains
unchanged. The number of surface proton sites in these catalysts can be assumed to be equal to
the total number of HPA protons (0.156 mmol gꢀ1 for HPW and 0.208 mmol gꢀ1 for HSiW).28
This allows for turnover frequencies (TOF) to be obtained. The TOF values (hꢀ1) were calculated
as reaction rate per single proton site. The reaction rate (r) was determined as r = XF/W (mol hꢀ
1gꢀ1), where X is the conversion of benzene and W/F = 80 g h molꢀ1 is the contact time. Figure 6
shows the plot of ln(TOF) versus ∆H for benzene alkylation, which demonstrates a fairly good
correlation between the turnover reaction rate and the catalyst acid strength. This backs up the
reaction mechanism through steps (1) and (2) (Scheme 1) and also supports the conclusion that at
Pt loading above 0.5% the reaction is limited by step (2) of benzene alkylation with propene,
whereas step (1) is at fast quasiꢀequilibrium.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Mechanism of formation of alkylated aromatic byꢀproducts in the alkylation of benzene by
ethane and propane over Pt/HZSMꢀ5 has been discussed in detail elsewhere.9ꢀ11,16 MePh and
EtPh, the main byꢀproducts in the alkylation with propane, are more favourable
thermodynamically than the desired iPrPh.4,16 These have been suggested to arise from acidꢀ
catalyzed cracking of propane as well as from cracking and transalkylation of propylbenzenes
(iPrPh and nPrPh).16 In the reaction with Pt/HSiW, only small amounts of EtPh (0.5ꢀ3%) and
nPrPh (2.1ꢀ3%) were formed together with unidentified C9+ aromatics (Table 3). As no propane
cracking was observed (Table 2) and no MePh found amongst the products (Table 3), the
ACS Paragon Plus Environment
18

Page 19 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
formation of EtPh may be viewed as the result of iPrPh cracking, which would also produce
methane. The latter was indeed found amongst the alkylation products. As to the nPrPh is
concerned, it is likely to come from acidꢀcatalyzed isomerization of iPrPh.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 4. Effect of support on alkylation of benzene with propane via bifunctional catalyzed
pathwaya
Catalystb
Conversionc
Aromatic selectivity (%)c
(%)
7.3
4.0
2.4
3.0
2.4
MePh EtPh iPrPh nPrPh C9+
7%Pt/C+15%HSiW/SiO2
7%Pt/C+15%HPW/SiO2
7%Pt/C+15%HPW/TiO2
7%Pt/C+15%HPW/Nb2O5
7%Pt/C+15%HPW/ZrO2
0
1.0
1.6
1.9
2.7
2.5
85.8 3.5
82.5 3.2
82.9 2.1
82.3 2.8
83.6 2.2
9.7
12.1
13.2
11.4
11.2
0.6
0
0.8
0.5
aReaction conditions: 300 oC, 1 bar pressure, 0.20 g catalyst, inlet molar ratio C6H6/C3H8 = 1:9,
10 mL minꢀ1 flow rate, W/F = 80 g h molꢀ1, 2 h time on stream; in situ catalyst preꢀtreatment at
300 oC/1 h in H2 flow, 10 mL minꢀ1). bUniform physical mixture 7%Pt/C (0.02 g) +
15%HPA/Support (0.18 g) with 0.7% Pt content. cConversion and selectivity values at 2 h time
on stream.
ACS Paragon Plus Environment
19

ACS Catalysis
Page 20 of 24
1
2
3
4
5
6
7
8
9
1.5
1.0
0.5
0.0
HSiW/SiO2
HPW/SiO2
HPW/Nb2O5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
HPW/TiO2
HPW/ZrO2
120
130
140
ꢀ∆H (kJ molꢀ1)
150
160
Figure 6. Plot of ln(TOF) vs. ∆H for benzene alkylation over 1:9 w/w mixture
7%Pt/C+15%HPA/Support at 300 oC.
4. Conclusions
The alkylation of benzene with propane to yield isopropylbenzene proceeds with high selectivity
over bifunctional metalꢀacid catalysts comprising Pt and Keggin heteropoly acid in a fixedꢀbed
reactor at 250ꢀ350 oC and 1 bar pressure. Most efficiently the reaction occurs over
Pt/H4SiW12O40/SiO2 catalyst, giving isopropylbenzene with 90ꢀ93% selectivity at 6ꢀ8% benzene
conversion at 300 oC and an inlet C6H6/C3H8 molar ratio of 1:9. This significantly exceeds the
efficiency of previously reported Pt/HZSMꢀ5 catalyst.16 The alkylation proceeds through the
bifunctional reaction pathway (Scheme 1) including dehydrogenation of propane to propene (1)
on Pt sites followed by benzene alkylation with propene (2) on acid sites. At Pt loadings above
0.5%, step (1) is at fast quasiꢀequilibrium, and step (2) is the rateꢀlimiting one. There is important
difference in performance between Pt/HPA/SiO2 and Pt/HZSMꢀ5 catalysts. With the Pt/HZSMꢀ
ACS Paragon Plus Environment
20

Page 21 of 24
ACS Catalysis
1
2
3
4
5
6
7
8
9
5, reaction selectivity is controlled by acidꢀcatalyzed transformations within zeolite microporous
structure (product shape selectivity), leading to preferential formation of nPrPh together with
cracking and transalkylation products such as MePh and EtPh rather that the desired iPrPh. In
contrast, the mesoporous Pt/HPA/SiO2 catalyst gives selectively iPrPh, i.e., the alkylation
product favoured from the carbenium ion mechanism. The preferred reactor design is a twoꢀbed
configuration involving Pt/C top (upstream) and HSiW/SiO2 bottom (downstream) catalyst bed,
providing better catalyst stability to deactivation as well as higher iPrPh selectivity. Further
research is underway to explore other alkane/arene systems and compare the results obtained
with the commercial systems for the production of alkylbenzenes.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ASSOCIATED CONTENT
Supporting Information. Thermodynamic calculations, reactor setup, reaction time courses,
DRIFT spectra and H2ꢀTPR results. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
* Corresponding author. Eꢀmail: kozhev@liverpool.ac.uk (I.V. Kozhevnikov)
ACKNOWLEDGMENT
We thank Shaqra University, Shaqra, Saudi Arabia for PhD studentship (A. Alotaibi).
REFERENCES
1. Shilov, A. E. Activation of Saturated Hydrocarbons by Transition Metal Complexes; Reidel:
Dordrecht, 1984.
ACS Paragon Plus Environment
21

ACS Catalysis
Page 22 of 24
1
2
3
4
5
6
2. Hashiguchi, B. G.; Bischof, S. M.; Konnick, M. M.; Periana, R. A. Acc. Chem. Res. 2012,
45, 885ꢀ898.
7
8
9
3. Caeiro, G.; Carvalho, R. H.; Wang, X.; Lemos, M. A. N. D. A.; Lemos, F.; Guisnet, M.;
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ramoa Ribeiro, F. J. Mol. Catal. A: Chem. 2006, 255, 131ꢀ158.
4. Weissermel, K.; Arpe, H.ꢀJ. Industrial Organic Chemistry; WileyꢀVCH: Weinheim,
Germany, 2003.
5. Olah, G. A.; Schilling, P.; Staral, J. S.; Halpern, Yu.; Olah, J. A. J. Am. Chem. Soc. 1975,
97, 6807ꢀ6810.
6. Bragin, O. V.; Shpiro, E. S.; Preobrazhensky, A. V.; Isaev, S. A.; Vasina, T. V.;
Dyusenbina, B. B.; Antoshin, G. V.; Minachev, K. M. Appl. Catal. 1986, 27, 219ꢀ231.
7. Smirnov, A. V.; Mazin, E. V.; Ponomoreva, O. A.; Yuschenko, V. V.; Knyazeva, E. E.;
Nesterenko, S. N.; Ivanova, I. I. J. Catal. 2001, 135, 153ꢀ160.
8. Kato, S.; Nakagawa, K.; Ikenaga, N.; Suzuki, T. Catal. Lett. 2001, 73, 175ꢀ180.
9. Lukyanov, D. B.; Vazhnova, T. J. Mol. Catal. A: Chem. 2008, 279, 128ꢀ132.
10. Lukyanov, D. B.; Vazhnova, T. J. Catal. 2008, 257, 382ꢀ389.
11. Chua, L. M.; Vazhnova, T.; Mays, T. J.; Lukyanov, D. B.; Rigby, S. P. J. Catal. 2010, 271,
401ꢀ412.
12. Ordomskiy, V. V.; Rodionova, L. I.; Ivanova, I. I.; Luck, F. ChemCatChem 2012, 4, 681ꢀ
686.
13. Wong, K. S.; Vazhnova, T.; Rigby, S. P.; Lukyanov, D. B. Appl. Catal. A 2013, 454, 137ꢀ
144.
ACS Paragon Plus Environment
22

Page 23 of 24
ACS Catalysis
1
2
3
4
5
6
14. Vazhnova, T.; Rigby, S. P.; Lukyanov, D. B. J. Catal. 2013, 301, 125ꢀ133.
15. Ivanova, I. I.; Blom, N.; Derouane, E. G. J. Mol. Catal. 1996, 109, 157ꢀ168.
7
8
9
16. Smirnov, A. V.; Mazin, E. V.; Yuschenko, V. V.; Knyazeva, E. E.; Nesterenko, S. N.;
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ivanova, I. I.; Galperin, L.; Jensen, R.; Bradley, S. J. Catal. 2000, 194, 266ꢀ277.
17. Abasov, S. I.; Babayeva, F. A.; Zarbaliyev, R. R.; Abbasova, G. G.; Tagiyev, D. B.;
Rustamov, M. I. Appl. Catal. A 2003, 251, 267ꢀ274.
18. Bigey, C.; Su, BꢀL. J. Mol. Catal. A: Chem. 2004, 209, 179ꢀ187.
19. Huang, X.; Sun. X.; Zhu, S.; Liu, Z. React. Kinet. Catal. Lett. 2007, 91, 385ꢀ390.
20. Babaeva, F. A.; Abasov, S. I.; Rustamov, M. I. Petrol. Chem. 2010, 50, 42ꢀ46.
21. Hetterley, R. D. ; Kozhevnikova, E. F.; Kozhevnikov, I. V. Chem. Commun. 2006, 782ꢀ784.
22. Alotaibi, M. A.; Kozhevnikova, E. F.; Kozhevnikov, I. V. J. Catal. 2012, 293, 141ꢀ144.
23. Alotaibi, M. A.; Kozhevnikova, E. F.; Kozhevnikov, I. V. Chem. Commun. 2012, 48, 7194ꢀ
7196.
24. Alotaibi, M. A.; Kozhevnikova, E. F.; Kozhevnikov, I. V. Appl. Catal. A 2012, 447-448, 32ꢀ
40.
25. Okuhara, T.; Mizuno, N.; Misono, M. Adv. Catal. 1996, 41, 113ꢀ252.
26. Kozhevnikov, I. V. Catalysis by Polyoxometalates; Wiley & Sons: Chichester, England,
2002.
27. Alsalme, A. M.; Wiper, P. V.; Khimyak, Y. Z.; Kozhevnikova, E. F.; Kozhevnikov, I. V. J.
Catal. 2010, 276, 181ꢀ189.
28. Alharbi, W.; Brown, E.; Kozhevnikova, E. F.; Kozhevnikov, I. V. J. Catal. 2014, 319, 174ꢀ
181.
ACS Paragon Plus Environment
23

ACS Catalysis
Page 24 of 24
1
2
3
4
29. Benson, J. E.; Hwang, H. S.; Boudart, M. J. Catal. 1973, 30, 146ꢀ153.
5
6
7
30. CRC Handbook of Chemistry and Physics; Haynes, W. M., ed.; CRC Press, 2012.
8
9
31. De Angelis, A.; Amarilli, S.; Berti, D.; Montanari, L.; Perego, C. J. Mol. Catal. A: Chem.
1999, 146, 37ꢀ44.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
32. Nowinska, K.; Fiedorow, R.; Adamiec, J. J. Chem. Soc. Faraday Trans. 1991, 87, 749ꢀ753.
33. Chao, J.; Wilhoit, R. C.; Zwolinski, B. J. J. Phys. Chem. Ref. Data 1973, 2, 427ꢀ437.
34. Chao, J.; Zwolinski, B. J. J. Phys. Chem. Ref. Data 1975, 4, 251ꢀ261.
35. Wagman, D. D.; Evans, W. H.; Parker, V. B.; Schumm, R. H.; Halow, I.; Bailey, S. M.;
Churney, K. L.; Nuttall, R. L. J. Phys. Chem. Ref. Data 1982, 11, 1ꢀ392.
36. Alberty, R. A. J. Phys. Chem. Ref. Data 1985, 14, 177ꢀ192.
37. Bardin, B. B.; Bordawekar, S. V.; Neurock, M.; Davis, R. J. J. Phys. Chem. B 1998, 102,
10817ꢀ10825.
38. Brandle, M; J. Sauer, J. J. Am. Chem. Soc., 1998, 120, 1556ꢀ1570.
Table of Contents Graphic
ACS Paragon Plus Environment
24